第15章 THE CHEMISTRY OF A CANDLE (II) 蜡烛的化学知识（II）

“BUT what becomes of the candle,” pursued Harry, “as it bums away? where does it go?”

“Nowhere, I should think. It burns to nothing.”

“Oh, dear, no!” said Harry; “everything goes somewhere. You can see it goes into smoke, which makes soot, for one thing. There are other things it goes into, not to be seen by merely looking, but you can get to see them by taking the right means. Just put your hand over the candle, uncle.”

“Thank you, my young gentleman, I would rather be excused.”

“Not close enough down to burn you, uncle; — higher up. There; — you feel a stream of hot air, so something seems to rise from the candle. Suppose you were to put a long glass lamp-chimney over the flame, and let the flame burn just within the end of it, as if it were a chimney, some of the hot steam would go up and pass out at the top, but a sort of dew would be left behind in the glass chimney, if the chimney was cold enough when you put it on. There are ways of collecting this dew; and when it is collected it turns out to be really water. I am not joking, uncle. Water is one of the things which the candle turns into while burning — water coming out of fire. In some light-houses, Professor Faraday says, two gallons of oil are burned in a single night; and if the windows are cold, the steam from the oil clouds them, and, in frosty weather, freezes into ice.”

“Water out of a candle, eh?” exclaimed Mr. Bagges “As hard to get, I should have thought, as blood out of s post. Where does it come from?”

“Part from the wax, and part from the air; and yet not a drop of it comes from either the air or the wax. What do you make of that, uncle”

“Eh? Oh, I'm no hand at riddles! Give it up.”

“No riddle at all, uncle. That which comes from the wax is a gas called hydrogen. We can obtain it from water by passing the steam of boiling water through a red-hot gun-barrel which contains a quantity of iron wire or turnings.Part of the steam will mix with the iron turnings, and change them into rust; and the other part, which comes out of the end of the barrel, will be hydrogen gas, and this part of the water we can set on fire.”

“Eh?” cried Mr. Bagges. “Upon my word! One of these days we shall have you setting the river on fire!”

“Nothing more easy,” said Harry. “When pure hydrogen bums, we get nothing but water. I should like to show you how light this hydrogen is; and I wish I had a small balloon to fill with it and send up to the ceiling; or a pipe full of it to blow soap-bubbles with, and show how much faster they rise than common ones blown with the breath.”

“So do I,” interposed Master Tom.

“And so,” resumed Harry, “hydrogen, you know, uncle is part of water, and just one-ninth part. The other eight parts are a gas also, called oxygen. This is a very curious gas. It won't bum in air at all itself, like gas from a lamp; but it has a wonderful power of making things bum that are lighted and put into it. A lighted candle put into a jar of oxygen blazes up directly, and is consumed before you can say Jack Robinson. Charcoal bums away in it as fast, with beautiful bright sparks;phosphorus burns with a light that would dazzle you to look at; and a piece of iron or steel, just made red-hot at the end first, may be burned in oxygen more quickly than a tick could be in common air. The experiment of burning things in oxygen beats any fire-works.”

“How funny that must be!” exclaimed Tom.

“Now we see, uncle,” Harry continued, “that water is hydrogen and oxygen united together; that water is got whenever hydrogen is burned in common air;that a candle won't burn without air; and that when a candle burns, there is hydrogen in it burning and forming water. Now, then, where does the hydrogen of the candle get the oxygen, to turn into water with it?”

“From the air, eh?”

“Just so. It is the oxygen in the air that makes things burn; but if the air were nothing but oxygen, a candle would not last above a minute.

“‘If a house were on fire in oxygen, ' as Professor Faraday said, ‘every iron bar, or, rather, every pillar, every nail and iron tool, and the grate itself; all the zinc and copper roofs, and leaden coverings, and gutters, and pipes, would consume and burn, increasing the combustion.’”

“That would be, indeed, ‘burning like a house on fire, ’” observed Mr. Bagges.

“But there is another gas, called nitrogen,” I said Harry “which is mixed with the air; and it is this which prevents a candle from burning out too fast.”

“Eh?” said Mr. Bagges. “Well, I do think we are under considerable obligations to nitrogen.”

“I have explained to you, uncle,” continued Harry “how a candle, in burning, turns into water. But it turns into something else besides that. The little bits of carbon that I told you about, which are burned in the flame of a candle, and which make the flame bright, mingle with the oxygen in burning, and form still another gas, called carbonic acid gas, which is very destructive to life when we breathe it. So you see that a candle-flame is vapour burning; and that the vapour, in burning, turns into water and carbonic acid gas.”

“Haven't you pretty nearly come to your candle's end?” said Mr. Wilkinson.

“Nearly. I only want to tell uncle that the burning of a candle is almost exactly like our breathing. Breathing is consuming oxygen, only not so fast as burning. In breathing, we throw out from our lungs water in the form of vapour, and carbonic acid gas, and take oxygen in. Oxygen is as necessary to support the life of the body as it is to keep up the flame of a candle.”

“Well,” said Mr. Bagges, “any more to tell us about the candle?”

“If I had time, I could tell you a great deal more that Professor Faraday said about oxygen, and hydrogen, and carbon, and water, and breathing; but you should go and hear him yourself, uncle.”

“Eh? well I think I shall. Some of us seniors may learn something from a juvenile lecture, at any rate if given by a Faraday. And now, my boy, I tell you what,” added Mr. Bagges; “I am very glad to find you so fond of study and science; and you deserve to be encouraged; and so I'll give you a — what-d'ye-call-it — a galvanic battery on your next birth-day; and so much for your teaching your old uncle the Chemistry of a Candle.”

Words

blazes,flames.

ceiling,Inside-roof.

collecting,gathering.

combustion,conflagration.

considerable,important.

deserve,merit.

destructive,injurious.

encouraged,stimulated.

exclaimed,ejaculated.

excused,pardoned.

experiment,operation.

explained,expounded.

freezes,congeals.

grate,fireplace.

increasing,augmenting.

joking,making fun.

obligation,indebtedness.

obtain,procure.

prevents,hinders.

pursued,continued.

quantity,portion.

riddies,conundrums.

seniors,old folks.

support,maintain.

suppose,assume.

turnings,flings.

united,Joined.

wonderful,extraordinary.

Questions

What are the different things into which the candle goes when it burns? How is the water produced? What is it that prevents the candle from burning too fast? How is the carbonic acid gas produced? Show how the burning of a candle resembles the process of breathing.

“那蜡烛会变成什么呢，”哈利继续追问，“它燃尽了之后会变成什么了呢？”

“什么也不是，我觉得。燃烧不成什么东西。”

“哦，亲爱的，不是的！”哈利说道，“所有的东西都会变成某种东西。你可以看见它变成了烟，变成烟灰，这是一个例子。它还可以变成其他的东西，但不是通过简单地看就能发现的，而是需要通过适当的方法才行。把您的手放到蜡烛上方，叔叔。”

“谢谢你，我的小绅士，我看还是算了吧。”

“不要太靠近，不会烧到您的，叔叔；——举得高点儿，就这样；——你会感觉到热空气流，因此似乎是蜡烛里有什么东西在上升。假设您把一个长长的玻璃灯罩，照在火焰上，让火焰在罩子的尾端燃烧，就好像这罩子是烟囱似的，一定会有热流向上走，从罩子的顶端冒出去，而在玻璃罩子中间会留下一点水珠，如果你把罩子放到火焰上的时候，它是凉的话，这些水珠可以通过一些办法来收集；当收集好了之后，它们就会变成真正的水。我不是在开玩笑，叔叔。水是蜡烛燃烧的时候产生的物质之一——从火中产生的水。在一些通亮的屋子里，法拉德教授说，一晚上能烧掉两加仑的油脂；如果窗子是凉的话，因为油脂燃烧产生的水就会笼罩在窗子上，天气寒冷的时候，就会结成霜冻。”

“蜡烛会产生水，嗯？”巴格斯先生惊诧道，“这很不可思议，我原本以为，嗯，这简直像柱子会产生血液那么不可思议。那么水是从哪里来的呢？”

“一部分是来自蜡，一部分是来自空气；但没有一滴是完全来自蜡或者空气的。您想明白了吗，叔叔？”

“嗯，哦，我还是想不明白，我放弃。”

“一点儿也不难，叔叔。蜡产生了一种叫氢气的气体。我们在装有铁线或铁屑的烧得红热的油水分离罐上，放上沸腾水的水蒸气，这样就能从水中得到氢气了。部分水蒸气会和铁屑混合，把它们变成铁锈；而其他蒸气则会从罐子的底部出去，变成氢气，而这部分的水我们则能把它点燃。”

“啊？”巴格斯先生喊道。“我敢说，总有一天你能把河给点燃喽！”

“没那么简单，”哈利说。“当纯氢气燃烧的时候，我们得到的只是水。我想给您展示一下，怎么点燃氢气；要是有一只装满氢气的小气球就好了，把它放飞到天花板那儿；或者有一只管子里头都是氢气，用它来吹出肥皂泡泡，然后我就能给您展示一下它们比装满空气的球或泡泡飞得要快多了。”

“我也是，”汤姆少爷插嘴道。

“因此，”哈利继续说道，“你知道的，叔叔，氢气是水的一部分，而且仅仅占到其中的九分之一。剩余的九分之八的部分也是一种气体，叫作氧气。这是一种很有意思的气体。和灯产生的气体一样，它在空气中不会自己燃烧；但对于那些点燃的，并放置到它中间的东西而言，它有一种强大的使它们燃烧的能力。一支点燃的蜡烛放到一个装满氧气的罐子里，会马上剧烈燃烧起来，在你还没说完杰克·罗宾逊几个字前就烧尽了。木炭在氧气中也燃烧得很快，还会产生美丽的耀眼的火花；磷燃烧的时候会产生一种强光，让人眼睛不能直视；一块铁或钢，一开始末端烧得通红，放到氧气中会快速燃烧，比一段木棍在空气中燃烧得还要快。在氧气中，燃烧物体做的实验，胜过了其他的燃烧实验。”

“那一定有趣极了！”汤姆叫道。

“现在我们明白了，叔叔，”哈利继续说道，“水是由氢气和氧气组成的，只要空气中有氢气燃烧就会产生水；而蜡烛没有空气不会燃烧；当蜡烛燃烧的时候，是里头的氢气在燃烧并形成水。现在，蜡烛中的氢气是如何获取氧气，从而和氧气一同变成水的呢？”

“从空气中，嗯。”

“没错。正是空气中的氧气让东西燃烧；但如果空气中只有氧气的话，一支蜡烛燃烧的时间都不到一分钟。”

“法拉德教授说，‘如果一座房子在氧气中起火了’，‘所有的铁栏杆，或者换种说法，所有的柱子，所有的钉子和铁质工具以及壁炉；全部的锌和铜制的屋顶，铅质的覆盖物，水沟，管道，都会起火燃烧，增加火势。’”

“的确如此，就像整座房子着火了一样，”巴格斯先生评价道。

“但还有另一种气体，叫作氮气，”哈利说，“它混杂在空气中，就是它使得蜡烛不会过快燃烧。”

“哦？”巴格斯先生说。“好的，我真的认为我们欠了氮气好大一个人情。”

“我已经和您解释过了，叔叔，”哈利继续说道，“一支蜡烛是如何在燃烧的过程中变成水的。但除了水之外，它还变成了其他的东西。我之前和您说过的小小碳离子的，它在蜡烛的火焰中燃烧，并使得火焰明亮发光。如果碳和氧气混合燃烧的话，就会形成另外一种气体，叫碳酸气体，人如果吸了这种气体的话，是非常有害的。所以，您明白了蜡烛产生的火焰是因为气体在燃烧；而那种燃烧着的气体，变成了水和碳酸气体。”

“你关于蜡烛的故事，快要讲完了吗？”威尔肯森夫人问道。

“快了。我只想告诉叔叔蜡烛的燃烧就和我们的呼吸几乎是一样的道理。呼吸消耗氧气，只不过赶不上燃烧时消耗氧气的速度。我们呼吸的时候从肺里释放出蒸汽形式的水以及碳酸气体，吸进的则是氧气。氧气对于蜡烛火焰燃烧就和它对于支持生命的作用一样必不可少。”

“好的，”巴格斯先生说，“你还有什么关于蜡烛的知识要说吗？”

“如果我有时间的话，我会告诉您更多法拉德教授讲述的关于氧气的知识，关于氢气、碳、水、呼吸的知识；但您应该去亲自听听他讲的，叔叔。”

“嗯？好我觉得我会去的。我们老年人能从年轻人讲的课中学到一些东西，不管是不是一位叫法拉德的教授讲的。现在，我的孩子，我告诉你，”巴格斯先生补充道，“我非常高兴，你能这么喜欢学习，这么喜欢科学；你值得夸奖；因此我将给你一个——叫什么来着——一块电池作为你明年的生日礼物；你给老叔叔讲的蜡烛的化学知识课就到这里告一段落吧。”